The Firebirds - a young adult fantasy by Harry Simpson

Seven middle school students with learning challenges fall asleep during a read aloud and wake up in an altered world. Prisoners of school, perfect clones sent home in their place, their principal a witch, they are foiled at their efforts to escape by a invisible bubble around the school. It appears to be an alien invasion, but their clones are talking. Clueless adults, heroic kids, high adventure, and an asteroid on a collision course with earth.